Modern applications increasingly demand the capability to manage high currents in a very small space and often in harsh environments, e.g. large temperature changes during the lifetime of the package. Particularly, in the automotive sector, due to the increasing electrification of functions the high current demand has increased enormously; e.g. inverter and E-motor drives for hybrid car applications, starter-generator applications, high power DC-DC converter or x-by-wire applications like electric power steering or electric braking. These applications need high current carrying capabilities on a minimum space challenging the state-of-the-art power modules in terms of achievable power density. To respond to the demand for high current applications, new technologies need to be developed to overcome the thermal and electrical limitations of the state-of-the-art power switch packages and power modules.
Progress in semiconductor processes and device design have extended the performance limits of semiconductor devices beyond the capabilities of the state-of-the-art packages. Therefore, newer state-of-the-art packaging technologies for power devices try to achieve low inductivity and better thermal connectivity to a heatsink through bond wireless connection techniques to maximize the thermal contact area of the power device to a heatsink and/or maximize the electrical connection of the device to a power terminal/leadframe.
U.S. Pat. No. 6,624,522, and U.S. patent application Ser. No. 11/641,270 both assigned to the assignee of the present application, disclose bond-wireless packaging techniques.
The concepts disclosed in the above follow a similar principle: By connecting the topside of the power device (especially the source or the emitter contact) to a larger metal area the package gains a higher current carrying capability, better thermal properties and a lower inductivity at the same time to achieve high power densities, good thermal performance, improved low inductivity and higher reliability.
The packaging concept disclosed in U.S. patent application Ser. No. 11/641,270 solves the main problems regarding thermal mismatch, bond wire inductance, high current carrying capability and package inductance.
The inductance of the packaged device is an important contributor to the final performance of the power device. State-of-the-art power modules normally try to reduce package resistance by minimizing Cu-leads and distances between various devices. It is especially important in applications which use IGBT devices as power switches that the so called free wheeling diode is connected to the corresponding IGBT using a low inductance connection. The diode is a “partner device” for the IGBT and carries the inductive current when the IGBT is switched off preventing the IGBT from break through due to inductive current flow. The typical combination of IGBT and diode is shown in FIG. 1.
It is a conventional packaging technique to solder and wire-bond the diode as close as possible to the IGBT on a substrate like a DBC, PCB or IMS in order to minimize parasitic inductance between the diode and the IGBT.
It is also a conventional packaging technique to co-package an IGBT and a diode in one package by soldering both devices on a shared leadframe, attach wire bonds and finally passivate this package with e.g. a mold plastic.